1. Field of the Invention
This invention relates to a tube expanding apparatus of the type which has a plurality of mandrels to be forced into a plurality of tubes for simultaneously conducting diametrical expansion thereof, and more particularly to an improved structure for readily removably mounting such mandrels in a tube expanding apparatus.
2. Description of the Prior Art
In general, tube expanding apparatuses of the above described type comprise a slide which is vertically movable as guided along upright posts, and a horizontal mounting plate fixed to the underside of the slide and suspendingly supporting a plurality of mandrels, as disclosed for example in Japanese Patent Application Laid-open No. 59-174234 (Laid-open Oct. 2, 1984; Application No. 58-46731; Applicant: Kyoshin Kogyo Kabushiki Kaisha; Inventor: Kensaku HOMMA).
More specifically, in the tube expanding apparatus of the above Laid-open Japanese Application, the mounting plate has in its wall thickness a plurality of passage holes and a plurality of diametrically larger accommodating bores positioned coaxially above the respective passage holes in communication therewith. Each of the mandrels penetrates through each of the passage holes and has an enlarged head loosely housed in each of the accommodating bores, so that the mandrels are non-fixedly supported by the mounting plate in a suspending manner. An abutment plate having a plurality of through-holes or perforations in corresponding relation to selected ones of the mandrels is replaceably interposed between the slide and the mounting plate. The perforations have a diameter which is larger than the diameter of the enlarged mandrel heads. As a result, despite descent of the slide the selected ones of the mandrels are allowed to ascend through the perforations and thereby remain idle during a tube expanding operation, whereas the remaining ones of the mandrels are lowered together with the slide because of engagement of their respective heads with the underside of the abutment plate to conduct diametrical expansion of tubes therebelow.
When the abutment plate is replaced by another abutment plate which is differently perforated, it is possible to alter the arrangement of effective (non-idle) ones of the mandrels in accordance with the arrangement of tubes without requiring removal of certain ones of the mandrels per se. Thus, the non-fixed mounting of the mandrels on the mounting plate is advantageous in that the tube expanding apparatus becomes applicable to various tube arrangements by simple replacement of the abutment plate.
On the other hand, it is often necessary to remove each of the mandrels from the mounting plate as for example for replacement by a dimensionally different mandrel or for repair. However, the above Japanese Application fails to give any suggestion as to how to provide for such a possibility.
FIG. 13 of the accompanying drawings illustrates one possible arrangement for removable mounting of mandrels in a tube expanding apparatus similar to that of the above Japanese Application.
Referring now to FIG. 13, a horizontal mounting plate 100 which is fixed to the underside of an unillustrated slide has in its wall thickness a passage hole 101 for each penetrating mandrel 102 and a diametrically larger accommodating bore 103 located concentrically above the passage hole in communication therewith. The accommodating bore 103 loosely houses an enlarged head cap 104 attached to the upper end of the mandrel 102 by means of a clamping bolt 105. A horizontal abutment plate 106 is disposed above the mounting plate 100 to come into abutment with the head cap 104 for preventing upward displacement of the mandrel 102, whereby a tube (not shown) therebelow is diametrically expanded upon descent of the slide or the mounting plate 100. Alternatively, the abutment plate 106 may have a perforation 107 which is larger in diameter than the head cap 104, so that the mandrel 107 is allowed to rise freely through the perforation 107 for the purpose previously described, as indicated in phantom lines.
According to the arrangement of FIG. 13, the mandrel 102 is removable from the mounting plate 100 and the head cap 104 by loosening the clamping bolt 105. However, this arrangement necessitates an operator to climb above the mounting plate 100 to loosen the clamping bolt 105, consequently requiring a lot of time and labor.
Japanese patent application Laid-open No. 60-3927 (Laid-open Jan. 10, 1985; Application No. 58-111651; Applicant: Daikin Kogyo Kabushiki Kaisha; Inventor: Takashi MIYAGAWA) discloses three types of mandrel mounting structure which enable easy removal of each mandrel, and these three types will now be described below respectively with reference to FIGS. 14 to 16 of the accompanying drawings.
In a first type illustrated in FIG. 14, a mounting plate 200 has internally threaded holes 201 into which externally threaded upper ends 203 of mandrels 202 are screwed. Thus, the mandrels 202 can be removed from the mounting plate 200 by simply turning them from below.
Despite simplicity in the removal of the mandrels 202, the first type has a vital disadvantage in that because the mandrels 202 are fixed to the mounting plate 200 in a mounted condition, there is no possibility for the mandrels 202 to move upward relative to the mounting plate 200 even if such is desired. Another drawback with the first type is that the mandrels 202 may be unexpectedly removed from the mounting plate 200 due to repetitive application, to the mandrels, of a rotational force during a tube expanding operation.
According to a second type illustrated in FIG. 15, a mounting plate 300 has an insertion hole 301 for receiving the upper end of each mandrel 302. The mounting plate 300 further has a lateral hole 303 into which is slidably fitted a spring biased engaging member 304. The upper end of the mandrel 302 is provided with a recess 305 with which the engaging member 304 releasably engages When the mandrel 302 is rotated through more than a specified angle, the engaging member 304 retracts into the lateral hole 303 to allow subsequent removal of the mandrel from the mounting plate 300.
The second type also has the same drawbacks as the first type since the mandrel 302 is fixed to the mounting plate 300 in a mounted condition. Further, the problem of unexpected removal of the mandrel 302 is more serious in the second type than in the first type because even a slight rotation of the mandrel can cause complete removal thereof.
In a third type shown in FIG. 16, a mounting plate 400 has a blind hole 401 for receiving the upper end of each mandrel 402. The blind hole 401 is formed with a surrounding annular groove 403 in which is fitted a radially outer half of a rubber ring 404. The upper end of the mandrel 402 is also provided with an annular groove 405 into which a radially inner half of the rubber ring 404 is fitted. Thus, the upper end of the mandrel 402 can be forced into and out of the rubber ring 404 due to elastic deformation thereof.
Similarly to the first and second types, the mandrel 402 of the third type is incapable of moving upward relative to the mounting plate 400. Further, because the rubber ring 404 provides an extremely limited retaining force, the mandrel 402 may fall off due simply to the weight of its own. Moreover, the mandrel 402, once forced into its counterpart tube (not shown) for diametrical expansion, will not return to its original raised position if the frictional force between the mandrel and the tube exceeds the retaining force of the rubber ring 404.